1. Field of the Invention
Embodiments relate to communication systems and have particular, but not exclusive application in Long Term Evolved Advanced LTE-A networks and systems. Embodiments have particular application to device-to-device (D2D) communications.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities. The communications may comprise, for example, communication of voice, electronic mail (email), text message, multimedia, other data and so on. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication network may be a local network. A user can access a communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE). A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling fixed or wireless access to a communication network or communications directly with other users. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. A user who has accessed a system may also be provided broadcast or multi-cast content. Non-limiting examples of the content include downloads, television and radio programs, videos, advertisements, various alerts and other information. Communication networks typically comprise a plurality of base stations, or Node Bs, with which a UE can communicate when located in a cell for which a base station has coverage. These are often under the control of a network controller.
In order to provide easier and faster communications, device-to-device (D2D) communications technologies are known which use radio resources of a hosting cellular system, whilst allowing two user equipments to communicate directly with each other when in radio contact; i.e. without routing via base stations, radio networks etc. Mobile cellular device-to-device (D2D) communications are also referred to as mobile-to-mobile (M2M), machine-to-machine (M2M), terminal-to-terminal (T2T) or peer-to-peer (T2T) communications.
Mobile cellular D2D communications may be assumed to use a licensed radio spectrum and eventually an unlicensed spectrum extension under control of supporting cellular systems, and may use the same radio resources of supporting cellular systems. The advantages of direct D2D communications into a cellular network includes reducing transmitter power consumption in both device and network, improving the spectrum efficiency and network resource utilization, and increasing cellular network capacity and coverage.
In cellular integrated D2D, as the same radio resources of supporting cellular system may be used for direct D2D communications, the D2D resource allocation is preferably under the control and management of the cellular system so as to avoid interference between cellular and D2D users. However, normal resource allocation, monitoring and control in current cellular networks are not designed for localised and distributed D2D communications in which user equipment data transmission (as well as control signaling) happen (at least in part) directly between two or multiple UEs. A particular user equipment may not be considered as “trusted” entity from the view of an operator's network; and thus when allowing more user equipment more distributed control e.g. in conducting direct D2D communications, this creates the threat of unauthorized usage of radio resources.
Prior art systems have so far assumed UEs in D2D communications to be simply connected to the same cellular network. Thus there has been no consideration to multi-operator and/or multi-radio systems and problems arising therefrom. However there may be scenarios in which UEs (capable of D2D communications using certain Radio Access Technology (RAT) are subscribers of different competing operators which provide cellular access using similar or different RAT in an overlapping service area.
The UEs in these scenarios may have to select to camp-in or connect to, different cells and systems to that of their home operator's networks, as the operators may not support roaming for mobile users due to roaming restrictions. Therefore, even when UEs are located within D2D range of each other, they may need to communicate with each other using the traditional, resource-consuming access nodes via their home networks which are then interconnected via PSTN or the Internet. If the UEs are communicating via independent or separated radio access networks of different cellular operators, it may be difficult for an independent network to decide or detect that communicating devices are close to each other and to evaluate whether to try to setup a D2D connection.